An antenna assembly

ABSTRACT

An RFID read antenna assembly (100) for use on a metal substrate (20) is used to read an RFID tag (22) carried by an article (12) positioned relative to the metal substrate. The antenna assembly comprises a high permeability layer (104) mountable to the metal substrate, an elongate carrier (114) mounted to the high permeability layer and defining a longitudinal axis (106), and at least one antenna coil (102) carried by the elongate carrier. The at least one antenna coil has a plurality of uniformly spaced transversely arranged portions (116) defining a sequence of antenna loops (105) of substantially constant width. The width of each antenna loop is substantially the same as the spacing between adjacent transversely arranged portions.

TECHNICAL FIELD

The present disclosure relates, generally, to an antenna assembly and,more particularly, to an RFID read antenna assembly for use with aninventory tracking system for use in tracking and/or locating articlescarrying RFID tags. The disclosure has particular, but not necessarilyexhaustive, application to an RFID read antenna assembly for use on ametal substrate to read an RFID tag carried by an article positionedrelative to the metal substrate.

BACKGROUND

Tracking and/or locating inventory allows for accurate stocktake to beperformed and for inventory to be located and retrieved quickly. RFIDtag interrogation is a convenient method for tracking and locatinginventory, since it does not require users to come into contact with theinventory and can be performed rapidly. Certain types of inventory, suchas medical inventory, is stored on metal substrates within an incubatoror a cabinet.

In addition, at times, RFID tags are randomly placed on articlesresulting in difficulty in an RFID read antenna reading the RFID tagwhen an article with its RFID tag is subsequently placed in the vicinityof the RFID read antenna.

It will be appreciated that, in this specification, reference to“tracking” is to be understood as including, where appropriate, locatingof suitably tagged articles within a receptacle.

Any discussion of documents, acts, materials, devices, articles or thelike which has been included in the present specification is not to betaken as an admission that any or all of these matters form part of theprior art base or were common general knowledge in the field relevant tothe present disclosure as it existed before the priority date of each ofthe appended claims.

SUMMARY

In a first aspect of the present disclosure, there is provided an RFIDread antenna assembly for use on a metal substrate to read an RFID tagcarried by an article positioned relative to the metal substrate, theantenna assembly comprising: a high permeability layer mountable to themetal substrate; an elongate carrier mounted to the high permeabilitylayer and defining a longitudinal axis; and at least one antenna coilcarried by the elongate carrier, the at least one antenna coil having aplurality of uniformly spaced transversely arranged portions defining asequence of antenna loops of substantially constant width, the width ofeach antenna loop being substantially the same as the spacing betweenadjacent transversely arranged portions.

Each transversely arranged portion may form a transverse part of one ofthe antenna loops of the at least one antenna coil. The at least oneantenna coil may have at least one pair of transversely arrangedportions which cross over each other to define a figure of eight-typeconfiguration to form at least one pair of contiguous antenna loops. Theat least one antenna coil may include a plurality of pairs of spaced,transversely arranged portions. The spacing between the pairs of thetransversely arranged portions of the at least one antenna coil may beconstant to form a sequence of antenna loops of substantially constantwidth. The sequence of contiguous antenna loops may define a series offigure of eight-type configurations.

A part of the at least one antenna coil may have a serpentineconfiguration. In this specification, unless the context clearlyindicates otherwise, the term “serpentine configuration” is to beunderstood as an arrangement where at least one of an outgoing conductoror a return conductor of the antenna coil has a zigzag- or squarewave-like configuration to form a sequence of stepped transitions.

A tag antenna of the RFID tag to be read may be elongate and configuredto be placed transversely across the carrier. A width of the tag antennamay approximate the width of each antenna loop of the at least oneantenna coil.

The antenna assembly may comprise at least two antenna coils arranged ina longitudinally staggered relationship on the carrier, the antennacoils having the same configuration as each other. The at least twoantenna coils may be configured to be driven sequentially. Instead, theat least two antenna coils may be configured to be driven out of phasewith each other. The antenna assembly above may comprise two antennacoils. The two antenna coils may be configured to be driven 90° out ofphase with each other.

The high permeability layer may comprise a locator configured tocooperate with a complementary feature of the metal substrate forlocating the high permeability layer relative to the metal substrate.The high permeability layer may be a ferrite layer.

The antenna assembly may comprise a connector which is configured to beelectrically connected to an RFID tag interrogator via a connectionarrangement. The metal substrate may be foraminous to facilitate fluidflow through the substrate and past an article arranged on thesubstrate. The high permeability layer and the elongate carrier may beconfigured to minimise disruption of the fluid flow past the article.

The high permeability layer may be a first layer. The antenna assemblymay include a second high permeability layer mountable, in functionallyaligned relationship with the first high permeability layer, to a secondmetal substrate arranged in spaced, superjacent or subjacentrelationship relative to the metal substrate carrying the first highpermeability layer.

In another non-limiting embodiment of the present disclosure, there isprovided an inventory tracking method for use with a metal substrate,the metal substrate carrying at least one antenna assembly, as describedabove, the method comprising: positioning an article relative to theantenna coil of the at least one antenna assembly, the article carryingan associated RFID tag and being positioned such that the associatedRFID tag and the antenna coil of the at least one antenna assembly arefunctionally aligned for the associated RFID tag to be interrogated byan RFID tag interrogator via the at least one antenna assembly; andinterrogating the associated RFID tag by driving the at least oneantenna assembly via the interrogator.

In a non-limiting embodiment in which the at least one antenna assemblycomprises at least two antenna coils, the method may comprise drivingthe at least two antenna coils of the at least one antenna assemblysequentially via the interrogator to interrogate the associated RFIDtag.

In a non-limiting embodiment in which the at least one antenna assemblycomprises at least two antenna coils, the method may comprise drivingthe at least two antenna coils of the at least one antenna assembly outof phase with each other via the interrogator to interrogate theassociated RFID tag.

The metal substrate may comprise a plurality of discrete elongatecompartments with each compartment having a longitudinal axis, anantenna assembly, as described above, being arranged in each one of thecompartments with the longitudinal axis of each antenna assembly beingsubstantially co-axial with the longitudinal axis of its associatedcompartment. The method may comprise arranging the article in itsassociated compartment such that an antenna coil of the associated RFIDtag is arranged transversely to the longitudinal axis of the antennaassembly.

In yet another aspect of the present disclosure, there is provided amethod of modifying a metal substrate for tracking inventory, the methodcomprising: electrically connecting at least one antenna assembly, asdescribed above, to an RFID tag interrogator; and mounting the at leastone antenna assembly to the metal substrate.

In still another aspect of the present disclosure, there is provided aninventory tracking system for use with a metal substrate, the systemcomprising: an RFID tag interrogator; and at least one antenna assembly,as described above, mounted to the metal substrate to communicate withthe interrogator.

The system may further comprise at least one RFID tag, the, or each,RFID tag being mountable to an article, the article, in use, beingpositioned relative to the metal substrate such that the RFID tag andthe antenna coil of the at least one antenna assembly are functionallyaligned for the associated RFID tag to be interrogated by theinterrogator via the antenna assembly.

The system may further include a connection arrangement via which the atleast one antenna assembly communicates with the interrogator. The metalsubstrate may be removably receivable in a holder. The connectionarrangement may include at least one connector for establishing, andbreaking, electrical contact between the at least one antenna assemblyand the interrogator when the metal substrate is inserted into, andremoved from, the holder, respectively. The metal substrate and theholder may include complementary retention elements for retaining andlocating the metal substrate in position relative to the holder when themetal substrate is inserted into the receiver to facilitate retention ofthe metal substrate relative to the holder on insertion of the metalsubstrate into the holder.

Throughout this specification the word “comprise”, or variations such as“comprises” or “comprising”, will be understood to imply the inclusionof a stated element, integer or step, or group of elements, integers orsteps, but not the exclusion of any other element, integer or step, orgroup of elements, integers or steps.

BRIEF DESCRIPTION OF DRAWINGS

Non-limiting embodiments of the disclosure will now be described by wayof example only with reference to the accompany drawings in which:

FIG. 1 shows a perspective view of a cabinet including a receptacle, aholder in the form of a frame arranged in the receptacle and metalsubstrates each in the form of a tray, removably received in the frame;

FIG. 2 shows a schematic, front view of a non-limiting embodiment of aninventory tracking system for use in tracking articles received on thetrays of the cabinet shown in FIG. 1 ;

FIG. 3 shows a plan view of one of the trays of the system shown in FIG.2 , in use, with four RFID read antenna assemblies of the inventorytracking system being mounted to the tray, and with four articles beingreceived on the tray, each article being associated with one of theantenna assemblies;

FIG. 4 shows a partial, schematic side view of one of the RFID readantenna assemblies mounted to the tray shown in FIG. 3 ;

FIG. 5 a shows atop view of a non-limiting embodiment of an antennaassembly for use with the tray of the system shown in FIG. 3 ;

FIG. 5 b shows a top view of an alternate non-limiting embodiment of anantenna assembly for use with the tray of the system shown in FIG. 3 ;

FIG. 6 shows a schematic, top view of another non-limiting embodiment ofan antenna assembly for use with the tray of the system shown in FIG. 3;

FIG. 7 a shows a sectional side view of a part of one non-limitingembodiment of the inventory tracking system mounted on one of the traysof the cabinet, in use, with an article carrying an RFID tag beingreceived on the tray;

FIG. 7 b shows a sectional side view of a part of another non-limitingembodiment of the inventory tracking system mounted on one of the traysof the cabinet, in use, with an article carrying an RFID tag beingreceived on the tray;

FIG. 8 shows a schematic, top view and a sectional view of the antennaassembly shown in FIG. 5 a , the sectional side view showing resultantmagnetic fields generated by the antenna coil of the antenna assembly,in use;

FIG. 9 a shows a schematic, perspective view of a part of a tag antennaof an RFID tag arranged relative to an antenna coil of the antennaassembly shown in FIG. 5 a , FIG. 5 b , and FIG. 6 , in use, showing theelectromagnetic coupling between the tag antenna and the antennaassembly;

FIG. 9 b shows a schematic, sectional, side view of the in useconfiguration shown in FIG. 9 a , showing the electromagnetic couplingbetween the tag antenna and the antenna assembly when the tag antenna isoffset relative to transversely arranged portions of the antenna coil ofthe antenna assembly of FIG. 5 a , FIG. 5 b , or FIG. 6 , in use;

FIG. 10 shows a schematic, sectional, side view of the antenna coilshown in FIG. 5 a or FIG. 5 b and a normalised mutual inductance vsposition plot of various positions of the tag antenna relative to theantenna coil of the antenna assembly, in use;

FIG. 11 shows a schematic, sectional, side view of the antenna coilsshown in FIG. 6 and a normalised mutual inductance vs position plot ofvarious positions of the tag antenna relative to the antenna coil of theantenna assembly, in use; and

FIG. 12 shows a schematic of various methods used to drive the antennacoils shown in FIG. 6 .

DETAILED DESCRIPTION OF NON-LIMITING EMBODIMENTS

In the drawings, reference numeral 10 generally designates anon-limiting embodiment of an inventory tracking system for use intracking articles 12 received in a cabinet 14. As shown in FIG. 1 , thecabinet 14 includes a receptacle 16, a holder in the form of a frame 18arranged in the receptacle 16, and doors 17. The cabinet 14 alsoincludes metal substrates, each in the form of a tray 20. The trays 20are displaceably and, more particularly, removably, received in theframe 18 and arranged in a spaced, operatively vertically stackedrelationship in the frame 18.

The non-limiting embodiment of the cabinet 14 shown in FIG. 1 is anincubator for articles 12, for example the cabinet 14 may be anagitator. Each article 12 may be in the form of a flexible, generallyplastics, bag containing bodily fluids, such as blood or bloodcomponents, for example, platelets. The contents of each bag needs to beagitated and, as such, the frame 18 is mounted within the receptacle 16of the cabinet in a reciprocatory manner to be reciprocated relative tothe receptacle 16 to effect agitation of the bags 12.

It will be appreciated by a person skilled in the art that, in othernon-limiting embodiments (not illustrated), there may only be a singletray 20 removably received in the frame 18, that there may only be asingle article 12 received on the tray 20, and/or that the cabinet 14may be any general cabinet with trays 20.

In the schematic representation of the inventory tracking system 10shown in FIG. 2 , each tray 20 is configured to receive a plurality ofthe bags 12 in operatively horizontally spaced relationship, each bag 12carrying an elongate RFID tag 22 arranged transversely across the bag12. Typically, an RFID tag may include an RFID chip and an antenna coil.The inventory tracking system 10 includes an electrical connectorarrangement 24 having complementary components in the form of conductorcarriers 26, 28, carried by the trays 20 and the frame 18, respectively.Each conductor carrier 26, 28 is in the form of a printed circuit board(PCB).

One PCB 26 is mounted to each tray 20 and carries a set of conductors(not shown) in the form of tracks of the PCB 26. One PCB 28 is mountedto each support stanchion 29 of the frame 18 and carries a second set ofconductors (not shown), also in the form of tracks of the PCB 28. PCB 26and PCB 28 are connected via electrical connection 36.

The inventory tracking system 10 also includes an RFID tag interrogator30 to which each of the PCBs 28 is connected, as representedschematically by wired electrical connection 32 as shown in FIG. 2 . TheRFID tag interrogator 30 is configured to interrogate the RFID tag 22 ofeach bag 12. The RFID tag interrogator 30 is connected to a computer(not shown) either via a wired or a wireless connection.

As indicated above, a PCB 26 is associated with each tray 20 tofacilitate interrogation of the RFID tag 22 of each bag 12 on each tray20 in the cabinet 14 by the RFID tag interrogator 30.

FIG. 3 shows a non-limiting embodiment of one of the trays 20 of thecabinet 14. The tray 20 carries a plurality of laterally arrangeddividers 21 defining a plurality of discrete elongate compartments 38,40, 42, 44 in each of which one of the bags 12, carrying the RFID tag22, is received.

The inventory tracking system 10 also includes a plurality of RFID readantenna assemblies 100, each of which is in accordance with anon-limiting embodiment of this disclosure and as will be described ingreater detail below. Each antenna assembly 100 is for use on the tray20 to read the RFID tag 22 carried by the bag 12 positioned relative tothe tray 20. In the non-limiting embodiment shown in FIG. 3 , an antennaassembly 100 is associated with each compartment 38, 40, 42, 44 of eachtray 20 of the cabinet 14.

Each antenna assembly 100 includes an antenna coil 102, a cover (notshown), a high permeability layer in the form of a ferrite layer 104,and an elongate carrier 114 (FIGS. 5 a and 5 b ). The antenna coil 102of each antenna assembly 100 terminates in a pair of contacts 110, 112via which the antenna assembly 100 connects to one of the PCBs 26.Further, each antenna assembly 100 is mounted to the tray 20, with theferrite layer 104, in this non-limiting embodiment (and also as shown inFIG. 7 a ), being disposed on an operatively upper surface 35 of thetray 20. Each bag 12 rests on its associated antenna assembly 100, inuse. The antenna assembly 100 is visible for compartment 42 in FIG. 3 ,with the absence of an article 12 therein for the purposes ofillustrating the antenna assembly 100 in compartment 42.

Each of the compartments 38, 40, 42, 44 is elongate and defines alongitudinal axis 46, and each antenna assembly 100 is correspondinglyelongate, with the elongate carrier 114 defining a longitudinal axis106. When the antenna assembly 100 is mounted in its associatedcompartment 38, 40, 42, 44, the longitudinal axis 106 of the antennaassembly 100 lies substantially coaxially with the longitudinal axis 46of its associated compartment 38, 40, 42, 44. In this way, the RFID tag22 of the bag 12 associated with that compartment 38, 40, 42, 44 and theantenna coil 102 of the antenna assembly 100 are functionally aligned tofacilitate interrogation of the RFID tag 22 by the RFID tag interrogator30 via the antenna assembly 100 of the compartment 38, 40, 42, 44. Itwill be understood that the functional alignment between the RFID tag 22and the antenna assembly 100 is achieved by arranging the bag 12 in itsassociated compartment 38, 40, 42, 44 such that an antenna coil of theassociated RFID tag 22 is arranged transversely to the longitudinal axis106 of the antenna assembly 100.

FIG. 5 a shows a first non-limiting embodiment of the antenna coil 102,which terminates in the pair of contacts 110, 112. The antenna coil 102communicates with, and is configured to be driven by, the RFID taginterrogator 30 via the pair of contacts 110, 112 and the connectorarrangement 24 to carry a current in the direction shown by arrows 118for interrogating the RFID tag 22. The ferrite layer 104 is mountable tothe tray 20 and the elongate carrier 114 is mounted to the ferrite layer104.

The antenna coil 102 is carried by the elongate carrier 114 and has aplurality of uniformly spaced transversely arranged portions 116defining a sequence of antenna loops 105 of substantially constantwidth. The width of each antenna loop 105 is substantially the same asthe spacing between adjacent transversely arranged portions 116. In thisnon-limiting embodiment, each transversely arranged portion 116 forms atransverse part of one of the antenna loops 105 of the antenna coil 102and the antenna coil 102 has a plurality of pairs of transverselyarranged portions 116 which cross over each other to define a series orsequence of figure of eight-type configurations, forming a sequence ofcontiguous antenna loops 105. It will be appreciated that, in thisnon-limiting embodiment, the spacing between the pairs of thetransversely arranged portions 116 of the antenna coil 102 is constantto form the sequence of substantially constant width antenna loops 105.

It will be understood by those skilled in the art that each pair oftransversely arranged portions 116 cross over each other by one of thetransversely arranged portions 116 passing through one side of thecarrier 114, which may be a PCB, to continue on an opposed side of theelongate carrier 114 while the other transversely arranged portionremains on top of the elongate carrier 114. Instead, the conductorsforming each transversely arranged portion 116 may be on the same sideof the PCB as each other but are electrically isolated from each otherwhere they cross each other.

It will be appreciated that, in this specification, reference to“contiguous antenna loops” is to be understood as a pair of antennaloops 105 which share a pair of the transversely arranged portions 116to be physically adjacent or neighbouring antenna loops 105. In theillustrated non-limiting embodiment, three such transversely arrangedportions 116 are provided. It will also be appreciated that there mayonly be a single pair of transversely arranged portions 116 defining asingle figure of eight-type configuration to form a single pair ofcontiguous antenna loops 105.

An alternative non-limiting embodiment is shown in FIG. 5 b . Withreference to previous non-limiting embodiments, like reference numeralsrefer to like parts, unless otherwise specified. The antenna coil 102has a plurality of uniformly spaced transversely arranged portions 116defining a sequence of spaced antenna loops 105 of substantiallyconstant width. The width of each antenna loop 105 is substantially thesame as the spacing between adjacent transversely arranged portions 116.In this non-limiting embodiment, an outgoing conductor 103 (from contact110) has a serpentine configuration (as defined above) and a returnconductor 107 (to contact 112) is substantially rectilinear for themajority of its length, running adjacent and parallel to one of thelongitudinal edges of the carrier 114. It will be appreciated that,instead, the return conductor 107 could adopt the serpentineconfiguration with the outgoing conductor 103 being rectilinear.

As described above, each bag 12, in use, carries blood platelets and itis important that the platelets be agitated while stored in the cabinet14. If the antenna assembly 100 were too thick, a step may be formed oneach side of the antenna assembly 100 and the surface 35 of theassociated tray 20. The bag 12 may overlie such a step and create adamming effect of the platelets at the step which is undesirable. Thus,in the case of each antenna assembly 100, each of the ferrite layer 104,the elongate carrier 114, and the cover has a thickness of less than 1mm, preferably about 0.1-0.5 mm, and, as an example, about 0.2 mm thickto reduce the size of the step and minimise damming of the platelets inthe bag 12.

It will be appreciated that there are multiple arrangements of theantenna assembly 100 within the frame 18 as a part of the inventorytracking system 10, which will provide an equivalent technical effect.

In the illustrated non-limiting embodiment, the tray 20 is foraminous tofacilitate fluid flow through the tray 20 and past any article 12arranged on the tray 20, and defining a plurality of apertures 48 asshown in FIG. 4 . In some embodiments, at least one of the apertures 48of the tray 20 forms a part of a locator mechanism 49. The antennaassembly 100 includes a second part of the locator mechanism 49, in theform of at least one locator pin 108, carried on an operatively bottomsurface of the ferrite layer 104. The locator pin 108 is removablyreceived in the aperture 48 to mount and locate the antenna assembly 100in its compartment 38, 40, 42, 44 of the tray 20. The locator pin 108 isretained in the aperture 48 via a press fit. It will be appreciated thateach antenna assembly 100 may comprise a plurality of longitudinallyand, optionally, laterally spaced locator pins 108, each locator pin 108being received in one of the plurality of apertures 48 of the tray 20.

In alternative embodiments, this type of locator mechanism is not used,and locator pins are not required. Instead, the antenna assembly 100 maybe configured to be of a shape and size to fit into the tray 20 securelywithout a locator mechanism.

FIG. 6 shows a second non-limiting embodiment of the antenna assembly100, with two antenna coils 102 a, 102 b arranged in a longitudinallystaggered relationship on the elongate carrier 114. With reference toprevious non-limiting embodiments, like reference numerals refer to likeparts, unless otherwise specified. The antenna coil 102 b is illustratedin dashed lines to clearly differentiate each antenna coil 102 a, 102 b.In addition, the two antenna coils 102 a, 102 b are shown with theirlongitudinal axes 120 a, 120 b offset from each other, the axes 120 a,120 b being in register with the longitudinal axis 106 of the elongatecarrier 114. However, this is for illustrative purposes only and, inpractice, the longitudinal axes 120 a, 120 b of the two antenna coils102 a, 102 b, respectively, will be coaxial with each other. The pairsof transversely arranged portions 116 of each antenna coil 102 a, 102 bare longitudinally spaced from each other. It will be understood thatthe transversely arranged portions 116 of each antenna coil 102 a, 102 bare arranged in a similar manner as described above with reference toFIG. 5 a.

The antenna coils 102 a, 102 b have the same configuration as eachother, which, in this non-limiting embodiment, is two pairs oftransversely arranged portions 116, forming a sequence of threecontiguous antenna loops 105. The antenna coils 102 a, 102 b eachterminate in a pair of contacts 110 a, 112 a, 110 b, 112 b. The antennacoils 102 a, 102 b each communicate with, and are configured to bedriven by, the RFID tag interrogator 30 via the pairs of contacts 110 a,112 a, 110 b, 112 b and the connector arrangement 24 to interrogate theRFID tag 22 associated with the bag 12. It will be appreciated that, inanother non-limiting embodiment, the transversely arranged portions 116of each antenna coil 102 a, 102 b may be arranged in a similar manner tothat shown in FIG. 5 b.

The antenna coils 102 a, 102 b are configured to be driven sequentiallywith respect to each other. Alternatively, the antenna coils 102 a, 102b are configured to be driven out of phase with each other and, moreparticularly, the antenna coils 102 a, 102 b are configured to be driven90° out of phase with each other. These configurations will be describedin more detail below. It will be understood by the person skilled in theart that there may be more than two antenna coils carried by theelongate carrier 114 in order to provide more spaced pairs oftransversely arranged portions 116 in which case, where the antennacoils are driven out of phase with each other, the phase differencebetween the driving current of the antenna coils will differcorrespondingly.

The antenna coils 102 a, 102 b of the non-limiting embodiment of theantenna assembly 100 shown in FIG. 6 may be driven in a number of ways.Three non-limiting examples of suitable methods which may be used areillustrated in FIG. 12 . In a first non-limiting embodiment, a drivingmethod 400 is used, which uses a single RFID tag interrogator 30 with aswitch 402 that is operable to switch between connections 404 a, 404 bat a suitable frequency to effectively drive the antenna coils 102 a,102 b sequentially.

In a second non-limiting embodiment, a driving method 500 is used, whichalso employs a single RFID tag interrogator 30 and a single, bifurcatingconnection 502 used to drive both of the antenna coils 102 a, 102 busing a single signal which is split into a +45° signal and a −45°signal in order to drive the antenna coils 102 a, 102 b 90° out of phasewith each other.

In a third non-limiting embodiment, a driving method 600 is used. Inthis non-limiting embodiment, the RFID interrogator comprises two RFIDtag drivers 30 a, 30 b connected to the antenna coils 102 a, 102 b,respectively, via associated connections 602 a, 602 b. Each RFID tagdriver 30 a, 30 b is configured to drive its associated antenna coil 102a, 102 b at a suitable frequency such that the antenna coils 102 a, 102b are driven 90° out of phase with each other.

In the non-limiting embodiment shown in FIG. 7 a , each antenna assembly100 has a second high permeability layer, in the form of a secondferrite layer, 62 associated with it. Each second high permeabilitylayer 62 is mounted to an operatively lower surface 33 of a superjacenttray 20 a by press fitting at least one locator pin (not shown) into oneof the plurality of apertures 48 via the operatively lower surface 33 ofthe tray 20 a. The second ferrite layer 62 is functionally aligned withthe antenna assembly 100 mounted to the surface 35 of the subjacent tray20 b in the manner shown in FIG. 4 . The second ferrite layer 62provides a low reluctance path for a magnetic field emanating from theantenna assembly 100, thereby enhancing mutual inductance between theantenna assembly 100 and the RFID tag 22 carried by the bag 12.

As described above, it is preferred that each antenna assembly 100 bemade as thin as possible. This can result in manufacturing complexityand there is a risk of damage to the antenna assembly 100 when it iscleaned or removed from its associated tray 20. FIG. 7 b shows anothernon-limiting embodiment of the system 10. With reference to the previousdrawings, like reference numerals refer to like parts, unless otherwisespecified.

In this non-limiting embodiment, each antenna assembly 100 is mounted tothe superjacent tray 20 a by press fitting the locator pin 108 into oneof the plurality of apertures 48 via the operatively lower surface 33 ofthe tray 20 a (in a similar manner as shown in FIG. 4 ). In thisnon-limiting embodiment, each antenna assembly 100, once again, has asecond ferrite layer 62 associated with it. Each second ferrite layer 62is mounted to the subjacent tray 20 b by press fitting at least onelocator pin (not shown) into one of the plurality of apertures 48 viathe operatively upper surface 35 of the subjacent tray 20 b tofunctionally align with its associated antenna assembly 100. The secondferrite layer 62 serves to provide a low reluctance path for a magneticfield emanating from the antenna assembly 100, thereby enhancing mutualinductance between the antenna assembly 100 and the RFID tag 22 carriedby the bag 12. The second ferrite layer 62 is thin, being of the orderof less than 1 mm thick and, for example, about 0.2 mm thick, therebyreducing the step and potential damming effect of the bag 12 overlyingthe ferrite layer 62. In this way, the elongate carrier 114 and theferrite layer 104 are configured to minimise disruption of the fluidflow past the bag 12.

This arrangement is advantageous due to obviating the need for theantenna assembly 100 to be as thin as possible and can, instead, bemanufactured using, firstly, a thicker ferrite layer 104 and, secondly,a thicker antenna coil 102. This non-limiting embodiment has the furtheradvantage that the thicker ferrite layer 104 further strengthens themagnetic field enhancing RFID operation between the antenna assembly 100and the RFID tag 22 carried by the bag 12. The thicker antenna coil 102is up to about 3.5 mm thick, for example, approximately 1.6 mm thick.The thicker ferrite layer 104 is up to about 2.5 mm thick, for example,between approximately 0.5 mm to 1 mm thick, and, typically, about 0.5 mmthick.

In alternative embodiments, a single ferrite layer may be used under theantenna. In such embodiments, a locator pin and second ferrite layer 62is not required.

In use, once the inventory tracking system 10 has been installed in thecabinet 14, the user places one bag 12 in each compartment of the tray20, with each bag 12 having an RFID tag 22 associated with it.

To interrogate the RFID tag 22 of each article 12, the user drives theantenna assemblies 100 of each tray 20 via the RFID tag interrogator 30and the electrical connector arrangement 24. As shown in the schematic,sectional view A-A of FIG. 8 , the user driving the antenna coil 102 ofthe antenna assembly 100 causes inductive coupling to occur, formingmagnetic fields 122 proximate each transversely arranged portion 116.Magnetic fields 122 of crossed-over transversely arranged portions 116add together to form a stronger resultant magnetic field 124 than themagnetic field 122.

In use, inductive coupling occurs between a tag antenna conductor 13 ofthe RFID tag 22 and the driven antenna coil/s 102 of the antennaassembly 100. Tag antenna conductor 13 as illustrated in the figuresrepresents the conductor that forms part of the antenna coil of RFID tag22. The mutual inductance M of a conductor of length l at a distance dfrom a current carrying conductor of length l is given as:

$M = {\frac{\mu_{0}l}{2\pi}\left( {{\ln\left( \frac{2l}{d} \right)} - 1} \right)}$

FIG. 9 a shows a schematic of the tag antenna conductor 13 directlyabove a pair of transversely arranged portions 116 of one of the antennacoils 102 of the antenna assembly 100. The effective, coupling length lof the tag antenna conductor 13 and the distance d are illustrated and,for purposes of explanation, the bag 12 is not shown. Further, for easeof explanation, the pair of transversely arranged portions 116 isillustrated with the conductors constituting the pair of transverselyarranged portions 116 being parallel to each other but not crossed over.The mutual inductance M1, M2 between each transversely arranged portion116 and the tag antenna conductor 13 is provided by the above formula.However, since there are two current carrying conductors, the mutualinductances M1, M2 add together to produce a total mutual inductanceM_(T), which is given as:

$M_{T} = {{M_{1} + M_{2}} = {\frac{\mu_{0}l}{\pi}\left( {{\ln\left( \frac{2l}{d} \right)} - 1} \right)}}$

FIG. 9 b shows a schematic illustration of a situation in which the tagantenna conductor 13 is offset with respect to a pair of transverselyarranged portions 116 of one of the antenna coils 102 of the antennaassembly 100 by an amount denoted as x. In this configuration, d iscalculated as follows: d²=h²+x². Thus, in this situation, the totalmutual inductance M_(T) between the antenna coil 102 and the tag antennaconductor 13 is reduced.

FIG. 10 shows the RFID tag 22 at varying, horizontal positions relativethe antenna assembly 100, with the bag 12 not shown, to illustrate thevariety of positions at which the user may place the bag 12 on the tray20. In this non-limiting embodiment, a width 64 of the tag antennaconductor 13 approximates a spacing 126 between adjacent pairs of thetransversely arranged portions 116 and, hence, a width of one of theantenna loops 105 of the antenna coil 102.

The total mutual inductance M_(T) and an absolute value of the totalmutual inductance |M_(T)| are plotted against the horizontal position xof the tag antenna conductor 13 of the RFID tag 22 along the antennaassembly 100 in a plot 200 in FIG. 10 . The absolute or normalised valueof the total mutual inductance |M_(T)| is shown as a solid line and thetotal mutual inductance M_(T) is shown as a dashed line on the plot 200.The plot 200 shows that the total mutual inductance M_(T) is 0 when thetag antenna conductor 13 is positioned approximately midway betweentransversely arranged portions 116 and is at a maximum when the tagantenna conductor 13 is positioned above transversely arranged portions116. As a result, when a tag antenna conductor 13 is positioned midwaybetween adjacent pairs of transversely arranged portions 116, there isno, or minimal, coupling between the tag antenna conductor 13 and theantenna assembly 100 and the tag antenna conductor 13 may not be able tobe read by the antenna assembly 100 of the system 10.

To reduce this problem, two longitudinally offset antenna coils areprovided as described above with reference to FIG. 6 of the drawings.FIG. 11 shows a schematic representation of an RFID tag 22 at varying,horizontal positions along the non-limiting embodiment of the antennaassembly 100 shown in FIG. 6 , with the bag 12 not shown. FIG. 11further illustrates the variety of positions at which the tag 22 may beplaced relative to the antenna assembly 100 on the tray 20.

The absolute, or normalised, value of the total mutual inductance|M_(T)| of each of the antenna coils 102 a, 102 b is plotted against thehorizontal position x of the tag antenna conductor 13 of the RFID tag 22along the antenna assembly 100 in a corresponding plot 300 in FIG. 11 .The absolute value of the total mutual inductance |M_(T)|_(a) fromantenna coil 102 a is shown as a dashed line and the absolute value ofthe total mutual inductance |M_(T)|_(b) from antenna coil 102 b is shownas a solid line in the plot 300. Advantageously, in this non-limitingembodiment, the total mutual inductance M_(T) produced in the tagantenna conductor 13 does not reach 0 since the tag antenna conductor 13is always in a position to couple to either of the antenna coils 102 a,102 b. In other words, the distance d from the tag antenna conductor 13and either of the antenna coils 102 a, 102 b is sufficiently small ateach horizontal position x of the tag antenna 22 to produce adequatemutual coupling to enable the antenna assembly 100 to read the tagantenna conductor 13.

Advantageously, the trays 20 within the incubator are foraminous andinclude the apertures 48 to allow for ventilation. The locator 108received in the aperture 48 reduces relative movement of the antennaassembly 100 and the RFID tag 22 of the bag 12 as the frame 18 isreciprocated relative to the cabinet 14, thereby assisting inmaintaining signal strength.

In addition, the RFID tag 22 is applied to its associated bag 12 as partof a label adhesively attached to an operatively outer surface of thebag 12. As the label could be applied anywhere on the outer surface ofthe bag 12, the RFID tag 22 may not optimally align with the antennaassembly 100 of the compartment of the tray 20 into which the bag 12 isplaced. The use of an elongate, strip antenna assembly 100 assists inminimising misalignment of the RFID tag 22 and the antenna assembly 100.Also, as it is required to pass temperature controlling fluid around thebag 12, the use of an elongate, strip antenna assembly 100 minimises thenumber of apertures 48 occluded by the antenna assembly 100 allowingventilation of the bag 12 to occur.

Advantageously, the antenna assembly 100, due to each transverselyarranged portion 116, provides a magnetic field 122 which facilitatesgeneration of a total mutual inductance M_(T) between the tag antennaconductor 13 and the antenna coil 102 which enables the tag antennaconductor 13 to be read by the antenna assembly 100. Further, thecrossing over of the pair of transversely arranged portions 116advantageously provides the stronger magnetic field 124 to increase theprevalence of the total mutual inductance M_(T). In addition, wheremultiple antenna coils are provided, driving those antenna coils eithersequentially or out of phase with each other facilitates reading of thetag antenna conductor 13 of the RFID tag 22 irrespective of thepositioning of the tag antenna conductor 13 relative to the antennaassembly 100.

In some embodiments, each tray 20 (or a group of trays, for example arow of trays) is associated with an indicator 11 configured to indicatestatus parameters associated with the tray 20. In one example embodimenteach tray includes a light panel or light indicator such as a lightemitting diode (LED), for example a two-colour LED.

In some example embodiments, the LED can have one colour and is used toindicate that the tray 20 is properly pushed home ensuring goodelectrical contact between PCB 26 and PCB 28. If contact is not madethen the LED does not light up. In other example embodiments, the LEDcan be configured to display a coded message, for example the LED may beprogrammed to flash to indicate fill status of the tray 20. Flashingcould mean, for example, that there are some empty positions on the tray20 so that the user can see immediately where to place platelet bags 12on a tray 20 with space (for example in empty compartment 42 asillustrated in FIG. 3 ).

In yet further example embodiments, a two-colour LED may be used andprogrammed to indicate various messages as required. For example, acombination of colour combinations, flashing combinations, or the likemay indicate one or more of the tray 20 being properly pushed home (ornot), fill status, trays requiring special attention, etc.

The LED indicator 11 allows the user to interact with the cabinet 14without needing any computer interface (for example). With thissimplified interface a user can simply observe the LED colour or code,and thereby know that the tray 20 is properly pushed in, which trayshave room for further bags 12, and which trays need special attention.

It is noted that the foregoing has outlined some of the more pertinentnon-limiting embodiments. It will be clear to those skilled in the artthat modifications to the disclosed non-limiting embodiments can beeffected without departing from the scope thereof. As such, thedescribed non-limiting embodiments ought to be considered as merelyillustrative of some of the more prominent features and applications.Other beneficial results can be realized by applying the non-limitingembodiments in a different manner or modifying them in ways known tothose familiar with the art. This includes the mixing and matching offeatures, elements and/or functions between various non-limitingembodiments being expressly contemplated herein so that a person ofordinary skill in the art would appreciate from this disclosure thatfeatures, elements and/or functions of one embodiment may beincorporated into another embodiment, as those skilled in the art wouldappreciate from this disclosure that features, elements and/or functionsof one embodiment may be incorporated into another embodiment asappropriate, unless described otherwise, above. Although the descriptionis made for particular arrangements and methods, the intent and conceptthereof may be suitable for and applicable to other arrangements andapplications.

1. An RFID read antenna assembly for use on a metal substrate to read anRFID tag carried by an article positioned relative to the metalsubstrate, the antenna assembly comprising: a high permeability layermountable to the metal substrate; an elongate carrier mounted to thehigh permeability layer and defining a longitudinal axis; and at leastone antenna coil carried by the elongate carrier, the at least oneantenna coil having a plurality of uniformly spaced transverselyarranged portions defining a sequence of antenna loops of substantiallyconstant width, the width of each antenna loop being substantially thesame as the spacing between adjacent transversely arranged portions. 2.The antenna assembly of claim 1 in which each transversely arrangedportion forms a transverse part of one of the antenna loops of the atleast one antenna coil and in which the at least one antenna coil has atleast one pair of transversely arranged portions which cross over eachother to define a figure of eight-type configuration to form at leastone pair of contiguous antenna loops.
 3. The antenna assembly of claim2, in which the at least one antenna coil includes a plurality of pairsof spaced, transversely arranged portions and in which the spacingbetween the pairs of the transversely arranged portions of the at leastone antenna coil is constant to form a sequence of antenna loops ofsubstantially constant width.
 4. The antenna assembly of claim 3 inwhich the sequence of contiguous antenna loops defines a series offigure of eight-type configurations.
 5. The antenna assembly of claim 1,in which a part of the at least one antenna coil has a serpentineconfiguration.
 6. The antenna assembly of claim 1, in which a tagantenna of the RFID tag to be read is elongate and is configured to beplaced transversely across the carrier and in which a width of the tagantenna approximates the width of each antenna loop of the at least oneantenna coil.
 7. The antenna assembly of claim 1, comprising at leasttwo antenna coils arranged in a longitudinally staggered relationship onthe carrier, the antenna coils having the same configuration as eachother.
 8. The antenna assembly of claim 7, in which the at least twoantenna coils are configured to be driven sequentially.
 9. The antennaassembly of claim 7, in which the at least two antenna coils areconfigured to be driven out of phase with each other.
 10. The antennaassembly of claim 9, which comprises two antenna coils, and in which thetwo antenna coils are configured to be driven 90° out of phase with eachother.
 11. The antenna assembly of claim 1, in which the highpermeability layer comprises a locator configured to cooperate with acomplementary feature of the metal substrate for locating the highpermeability layer relative to the metal substrate.
 12. The antennaassembly of claim 1, in which the high permeability layer is a ferritelayer.
 13. The antenna assembly of claim 1, which comprises a connectorwhich is configured to be electrically connected to an RFID taginterrogator via a connection arrangement.
 14. The antenna assembly ofclaim 1, in which the metal substrate is foraminous to facilitate fluidflow through the substrate and past an article arranged on the substrateand in which the high permeability layer and the elongate carrier areconfigured to minimise disruption of the fluid flow past the article.15. The antenna assembly of claim 1 in which the high permeability layeris a first layer and in which the antenna assembly includes a secondhigh permeability layer mountable, in functionally aligned relationshipwith the first high permeability layer, to a second metal substratearranged in spaced, superjacent or subjacent relationship relative tothe metal substrate carrying the first high permeability layer.
 16. Aninventory tracking method for use with a metal substrate, the metalsubstrate carrying at least one antenna assembly, as claimed in claim 1,the method comprising: positioning an article relative to the antennacoil of the at least one antenna assembly, the article carrying anassociated RFID tag and being positioned such that the associated RFIDtag and the antenna coil of the at least one antenna assembly arefunctionally aligned for the associated RFID tag to be interrogated byan RFID tag interrogator via the at least one antenna assembly; andinterrogating the associated RFID tag by driving the at least oneantenna assembly via the interrogator.
 17. The method of claim 16, whichcomprises driving the at least two antenna coils of the at least oneantenna assembly, sequentially via the interrogator to interrogate theassociated RFID tag.
 18. The method of claim 16, which comprises drivingthe at least two antenna coils of the at least one antenna assembly, outof phase with each other via the interrogator to interrogate theassociated RFID tag.
 19. The method of claim 16, in which the metalsubstrate comprises a plurality of discrete elongate compartments witheach compartment having a longitudinal axis, an antenna assembly beingarranged in each one of the compartments with the longitudinal axis ofeach antenna assembly being substantially co-axial with the longitudinalaxis of its associated compartment, and in which the method comprisesarranging the article in its associated compartment such that an antennacoil of the associated RFID tag is arranged transversely to thelongitudinal axis of the antenna assembly.
 20. A method of modifying ametal substrate for tracking inventory, the method comprising:electrically connecting at least one antenna assembly, as claimed inclaim 1, to an RFID tag interrogator; and mounting the at least oneantenna assembly to the metal substrate.
 21. An inventory trackingsystem for use with a metal substrate, the system comprising: an RFIDtag interrogator; and at least one antenna assembly, as claimed in claim1, mounted to the metal substrate to communicate with the interrogator.22. The system of claim 21, further comprising at least one RFID tag,the, or each, RFID tag being mountable to an article, the article, inuse, being positioned relative to the metal substrate such that the RFIDtag and the antenna coil of the at least one antenna assembly arefunctionally aligned for the associated RFID tag to be interrogated bythe interrogator via the antenna assembly.
 23. The system of claim 21which includes a connection arrangement via which the at least oneantenna assembly communicates with the interrogator.
 24. The system ofclaim 23 in which the metal substrate is removably receivable in aholder and in which the connection arrangement includes at least oneconnector for establishing, and breaking, electrical contact between theat least one antenna assembly and the interrogator when the metalsubstrate is inserted into, and removed from, the holder, respectively.25. The system of claim 24 in which the metal substrate and the holderinclude complementary retention elements for retaining and locating themetal substrate in position relative to the holder when the metalsubstrate is inserted into the receiver to facilitate retention of themetal substrate relative to the holder on insertion of the metalsubstrate into the holder.